Series regulated power supply for arc discharge lamps utilizing incandescent lamps

ABSTRACT

A series regulated power supply for an arc discharge lamp is disclosed whereby at least one incandescent lamp is connected in series with the arc discharge lamp to establish a first current level. At least one other incandescent lamp is connected in shunt with the first lamp to establish a second current level. The incandescent lamps provide current regulation for the arc discharge lamp.

Elnited States Patent 1191 Caprari 1 SERIES REGULATED POWER SUPPLY FOR ARC DISCHARGE LAMPS UTILIZING INCANDESCENT LAMPS [75] Inventor: Fausto Caprari, Jersey City, NJ. [73] Assignee: RCA Corporation, New York, NY.

[22] Filed: July 21, 1972 [21] Appl. No.: 273,750

[52] US. Cl 315/205, 315/49, 315/72 [51] Int. Cl. H051! 37/00 [58] Field of Search 315/D1G. 5 DIG. 7, 58, 315/71, 72, 179 205, 149, 15 2, 49

[56] References Cited UNITED STATES PATENTS 2,020,737 11/1935 Pirani et a1. 315/49 1451 May 28, 1974 2,327,755 8/1943 Abernathy 315/179 x 1/1961 Lanata 315/49 X Primary Examiner1-1. K. Saalbach Assistant Examiner-Lawrence J. Dahl Attorney, Agent, or Firm-Edward J. Norton; Joseph S. Tripoli [57] ABSTRACT A series regulated power supply for an arc discharge lamp is disclosed whereby at least one incandescent lamp is connected in series with the arc discharge lamp to establish a first current level. At least one other incandescent lamp is connected in shunt with the first lamp to establish a second current level. The incandescent lamps provide current regulation for the arc discharge lamp.

8 Claims, 2 Drawing Figures SHU'TER CONTROL PAIENTEMYZB m V 3313576 h L1//L2//L3//L4 I OPERATING 2 U III, R STANDBY CURRENT 1 2 RMS ,1 l 1 I EIOPERATING VOLTAGE ERMS Fig. 2.

The present invention relates generally to power supplies for are discharge lamps and more particularly to a series current regulated supply utilizing incandescent lamps for the current regulating element.

Power supplies of the type discussed herein are especially useful in the field of photolithography. That is, applications where a photoresist substance must be exposed to a certain light intensity. Power supplies of this general nature may be found in the production of integrated circuits and printed circuit boards. In such applications it is extremely important to expose the light sensitive substances to the same light intensity throughout a production run. In terms of the source which energizes the light, such as an arc discharge lamp, it-is important to supply the lamp with substantially thesame current for each exposure operation. throughout the production run.

The usual series pass element in the prior art, for

power supplies of the present type, is an inductive circuit element. One of the problems with the utilization of an inductive element, or a plurality of inductive elements, as the series pass device is that the high voltage transients generated by the collapsing field drastically reduces the life of the arc discharge lamp.

Another prior art arrangement is the utilization of a ballast resistor in series with the arc discharge lamp. This arrangement, however, does not provide any current regulation for the arc discharge lamp.

The present invention provides a power supply with good current regulation as well as insuring a long life for the light source. Another advantage of the present invention is its low cost and light weight due to the arrangement of the circuit elements.

In accordance with the present invention acircuit isv provided for operating an arcdischarge lamp from a source of potential. The discharge lamp passes a first current level during one condition and a second current level during a second condition. Thecircu'it comprises at least one'incandescent lamp which is connected in series with the arc discharge lamp, for establishing the first current level. At least one other incandescent lamp is also provided. Means are provided for connecting the at least one other lamp in shunt with the at least one lamp for establishing the second current level.

IN THE DRAWING FIG. 1 is a partial schematic and partial block diagram of the preferred embodiment of the invention; and

FIG. 2 is a graph which compares the ballast characteristics of an inductor, a resistor-and an incandescent lamp.

Referring now to FIG. 1, there is provided a pair of input terminals 10 and 11 and a ground terminal 12. In the particular embodiment shown in FIG. 1 the signal applied to input terminals 10 and 11' is a 220 volt, 60 Hz signal.

A first plurality of incandescent lamps LI and L, are connected in parallel with each other and one end of the parallel combination is connected to input terminal 10.

The other end of the parallel combination of incandescent lamps L and L is connected to one terminal 13 of an arc discharge lamp 14. In the particular embodiment shown,,arc discharge lamp I4 is a-mercury arc lamp having the commercial designation l-I lOOA 4/T. The other terminal 15 of the arc lamp 14 has a connection back to input terminal 11.

Thecircuit thus far described shows a plurality of parallel connected incandescent lamps L, and L connected in series relationship'with the main light source, namely arc discharge lamp I4.

There is also provided a second bank or plurality of parallel connected incandescent lamps L and L One end of the parallel combination of lamps L and L is also connected to input terminal It). The other end of the parallel combination of lamps L and L is con-. nected to a normally open switching device 8 Switching device S may be a mechanical switch, such as arelay, or an electrical switch, such as a thyristor. The function of switch S is to provide a connecting means between the first plurality of incandescent lamps L and L and the second plurality of incandescent lamps L and L; such that when the switch S is selectively closed all of the'incandescent lamps will be in parallel with each other with the total parallel combination of lamps L L in series with the arc discharge lamp 114. In theembodiment of FIG. I, the incandescent lamps used are watt, 230 volt commercially available lamps.-

In addition, there is provided a movable shutter SH. In one position the shutter SI-I substantially blocks the light emanating from are discharge lamp 14 while in another position the shutter SI-I substantially passes the lightfrom arc discharge lamp 14. A shutter control mechanism 16 is provided to move the shutter SH from its normally light blocking position to its light passing 6 0 Hz, and switch S is open, a certain current level is established through the arc discharge lamp 14. This certain current level is termed the standby current and is determined by the number and type of incandescent lamps in series with the arc lamp I4.

The standby current illuminates incandescent lamps L and L and preferably is high enough to just start the arc discharge lamp glowing. At this time the shutter SI-I is in its normally blocking position and therefore little,

if any, light from the lamp 14 shines on the photoresist material (not shown) which is to be exposed.

Now the timer 1? is set for the desired length of time which may be of the order of seconds or minutes depending upon the type of photoresist material to be exposed. The operation of the timer 17 causes the switch S to close and the shutter SI-I to move to the nonblocking position. With switch S closed a new current level through lamp 14 is established and the desired light intensity, depending upon the new current level,

is allowed to shine on the photoresist material. The sec- 7 in each case the curves show the current-voltage characteristic for the particular arrangement which is to be placed in series with the arc discharge lamp.

The curves show that for the operating voltage E (RMS) which appears across lamps L, and L a certain standby current level I, (RMS) is obtained. When lamps L and L. are switched or connected into the system a second current level I: (RMS), which is the operating current level, is established.

Since the incandescent lamps exhibit a leveling off characteristic, i.e.,' small changes of current for changes of potential around the operating voltage E the circuit shown in FIG. 1 provides a current regulating function. The curves show that the regulation provided by the incandescent lamps is substantially better than that which would occur from the use of an inductor or a resistor in series with the arc lamp 14.

It will be evident from the foregoing that one may select the number and wattage of the incandescent lamps to establish any desired first and second current levels for the arc lamp l4.

In actual practice the arc lamp 14 previously mentioned was operated at 150 watts during the standby condition and 300 watts during the exposure condition. Thus, by not being forced to stay on at the higher output level on a continuous basis, the useful life of the arc discharge lamps is significantly extended.

in addition, it has been found'that the operation of arc discharge lamps at higher than rated levels,for short periods of time, as in the present application, does not shorten the life span of the lamp.

Finally, the disclosed arrangement provides an additional advantage in that the natural characteristic of the incandescent lamps provides a surge current at turn-on which is helpful in starting the arc discharge lamp.

What is claimed is:.

l. A circuit for operating an arc discharge lamp, from a source of potential, said arc discharge lamp passing a first level of current conduction during one condition and a second level of current conduction during a second condition, said circuit comprising:

at least one incandescent lamp connected in series with said are discharge lamp for establishing said first current conduction level;

at least one other incandescent lamp;

first means for connecting said at least one other incandescent lamp in shunt with said at least one incandescent lamp for establishing said second current conduction level; and

second means, operatively coupled to said first means, for substantially blocking the light from said are discharge lamp during said first level of current conduction and for substantially passing the light from said arc discharge lamp during said second level of current conduction.

2. The circuit according to claim 1 wherein said second means comprises a movable shutter means in proximity with said are discharge lamp, said shutter means being positioned to substantially block the light from said are dischargelamp when the current through said discharge lamp'is at said first level of current conduction and said shutter means being positioned to substantially pass the light from said are discharge lamp when the current through said are discharge lamp is at said second level of conduction.

3. The circuit according to claim 2 further comprising means for operatively coupling said shutter means and said connecting means for simultaneously passing the light from said are discharge lamp. and establishing said second current level.

4. The circuit according to claim 3 wherein said means for coupling the shutter means and said connecting means includes a timing means for maintaining said second means, operatively coupled to said first second current level through saidarc discharge lamp for a predetermined period of time.

5. The circuit comprising:

a pair of inputterminals adapted for connection to a source of alternating potential;

an arc discharge lamp connected in series circuit wit said input terminals;

a first plurality of parallel-connected incandescent lamps connectedin series with said are discharge lamp for establishing .a first level of current conduction through saidarc discharge lamp;

a second plurality of parallel connected incandescent lamps;

first means for selectively connecting said second plurality of lamps in parallel with saidfirst plurality of lamps for establishing a second level of current conductionygreater than said first current conduction level, through said are discharge lamp; and

means, for substantially blocking the light from said are discharge lamp during said first level of current conduction and for substantially passing the light from said are discharge lamp during said second level of current conduction.

6. The circuit according to claim 5 wherein said second means comprises a shutter means in proximity with said are discharge lamp and being arranged to block' the light from said are discharge lamp when the current through the arc discharge lamp is at said first level of current conduction and said shutter means being positioned to pass the light from said are discharge lamp when the current through said arc discharge lamp is at a said second level of conduction.

7. The circuit according to claim 6 further comprising means for operatively coupling said shutter means and said connecting means for simultaneously passing the light from said are discharge lamp and establishing said second current level. I

8. The circuit according to claim 7 wherein said means for operatively coupling said shutter means and maintaining said second current level for a predetermined period of time. 

1. A circuit for operating an arc discharge lamp, from a source of potential, said arc discharge lamp passing a first level of current conduction during one condition and a second level of current conduction during a second condition, said circuit comprising: at least one incandescent lamp connected in series with said arc discharge lamp for establishing said first current conduction level; at least one other incandescent lamp; first means for connecting said at least one other incandescent lamp in shunt with said at least one incandescent lamp for establishing said second current conduction level; and second means, operatively coupled to said first means, for substantially blocking the light from said arc discharge lamp during said first level of current conduction and for substantially passing the light from said arc discharge lamp during said second level of current conduction.
 2. The circuit according to claim 1 wherein said second means comprises a movable shutter means in proximity with said arc discharge lamp, said shutter means being positioned to substantially block the light from said arc discharge lamp when the current through said discharge lamp is at said first level of current conduction and said shutter means being positioned to substantially pass the light from said arc discharge lamp when the current through said arc discharge lamp is at said second level of conduction.
 3. The circuit according to claim 2 further comprising means for operatively coupling said shutter means and said connecting means for simultaneously passing the light from said arc discharge lamp and establishing said second current level.
 4. The circuit according to claim 3 wherein said means for coupling the shutter means and said connecting means includes a timing means for maintaining said second current level through said arc discharge lamp for a predetermined period of time.
 5. The circuit comprising: a pair of input terminals adapted for connection to a source of alternating potential; An arc discharge lamp connected in series circuit with said input terminals; a first plurality of parallel connected incandescent lamps connected in series with said arc discharge lamp for establishing a first level of current conduction through said arc discharge lamp; a second plurality of parallel connected incandescent lamps; first means for selectively connecting said second plurality of lamps in parallel with said first plurality of lamps for establishing a second level of current conduction, greater than said first current conduction level, through said arc discharge lamp; and second means, operatively coupled to said first means, for substantially blocking the light from said arc discharge lamp during said first level of current conduction and for substantially passing the light from said arc discharge lamp during said second level of current conduction.
 6. The circuit according to claim 5 wherein said second means comprises a shutter means in proximity with said arc discharge lamp and being arranged to block the light from said arc discharge lamp when the current through the arc discharge lamp is at said first level of current conduction and said shutter means being positioned to pass the light from said arc discharge lamp when the current through said arc discharge lamp is at a said second level of conduction.
 7. The circuit according to claim 6 further comprising means for operatively coupling said shutter means and said connecting means for simultaneously passing the light from said arc discharge lamp and establishing said second current level.
 8. The circuit according to claim 7 wherein said means for operatively coupling said shutter means and said connecting means includes a timing means for maintaining said second current level for a predetermined period of time. 